package/lldpd: disable use of libbsd

libbsd installs at least one .pc file that contains a -isystem include
path (-isystem /usr.include/bsd), but -isystem is not munged by
pkg-config, so we end up using /usr/include/bsd which is not suitable
for the target. And breaks big time (see failures, below).

But using libbsd is completely optional. In fact, our lldpd.mk did not
even express the dependency on libbsd, so we may well have had builds
without libbsd.

The functionality brought in by using libbsd is very minor (just setting
the neighbour name in /proc/self/cmdline), so we just make lldpd not use
libbsd at all. There is no --disable-libbsd or such, so we just patch it
out of configure.ac.

Fixes:
    http://autobuild.buildroot.org/results/6b7/6b70fa379e834ec71cc260ba6af771b531ca3511/
    http://autobuild.buildroot.org/results/769/769074c4bb67336ae6679f2c1cd2a8220d2bec24/
    http://autobuild.buildroot.org/results/c8a/c8a6001f437701ecc75f6c9252935645bda8a8c8/


    [...]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>